arm64: Honor VHE being disabled from the command-line

Finally we can check whether VHE is disabled on the command line,
and not enable it if that's the user's wish.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: David Brazdil <dbrazdil@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210208095732.3267263-16-maz@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/asm-offsets.c

@@ -99,6 +99,9 @@ int main(void)
   DEFINE(CPU_BOOT_STACK,	offsetof(struct secondary_data, stack));
   DEFINE(CPU_BOOT_TASK,		offsetof(struct secondary_data, task));
   BLANK();
+  DEFINE(FTR_OVR_VAL_OFFSET,	offsetof(struct arm64_ftr_override, val));
+  DEFINE(FTR_OVR_MASK_OFFSET,	offsetof(struct arm64_ftr_override, mask));
+  BLANK();
 #ifdef CONFIG_KVM
   DEFINE(VCPU_CONTEXT,		offsetof(struct kvm_vcpu, arch.ctxt));
   DEFINE(VCPU_FAULT_DISR,	offsetof(struct kvm_vcpu, arch.fault.disr_el1));

arch/arm64/kernel/hyp-stub.S

@@ -87,6 +87,17 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
 	ubfx	x1, x1, #ID_AA64MMFR1_VHE_SHIFT, #4
 	cbz	x1, 1f
 
+	// Check whether VHE is disabled from the command line
+	adr_l	x1, id_aa64mmfr1_override
+	ldr	x2, [x1, FTR_OVR_VAL_OFFSET]
+	ldr	x1, [x1, FTR_OVR_MASK_OFFSET]
+	ubfx	x2, x2, #ID_AA64MMFR1_VHE_SHIFT, #4
+	ubfx	x1, x1, #ID_AA64MMFR1_VHE_SHIFT, #4
+	cmp	x1, xzr
+	and	x2, x2, x1
+	csinv	x2, x2, xzr, ne
+	cbz	x2, 1f
+
 	// Engage the VHE magic!
 	mov_q	x0, HCR_HOST_VHE_FLAGS
 	msr	hcr_el2, x0